Distribution of ploidy in prokaryotes and evolutionary advantages of polyploidy in prokaryotes

真核生物是典型的二倍体生物，一些真核生物群包含许多多倍体物种。相比之下，原核生物通常被认为是单倍体，含有一个环形染色体分子。然而，最近发现两种不同属的嗜盐古菌是高度多倍体的(Breuert，Alners，Spohn和Soppa 2006，PLoS One，E92)。一项文献调查显示，只有极少数物种的倍性水平被确定。其中超过一半的人有几个染色体副本，这表明多倍体在原核生物中可能比预期的更普遍。该项目的一部分将解决多倍体的分布问题。将确定代表不同细菌系统类群的大约15个模式物种的倍性水平。此外，还将对环境样品中的新菌株进行鉴定，并尝试选择多倍体细菌物种。该项目的第二部分将讨论多倍体的进化优势。首先，将选择可以与野生型进行比较的嗜盐古生菌的倍性突变体。将表征其对X射线照射和干燥的耐受性。将证明细胞内多态在特定条件下可以产生选择优势，并将进行基因转换研究。综上所述，该项目挑战了教科书上认为原核生物通常是单倍体的观点，并将深入了解原核生物多倍体的进化优势。

Eukaryotes are typically diploid, and some eukaryotic groups contain many polyploid species. In contrast, prokaryotes are generally believed to be monoploid and contain one molecule of a circular chromosome. However, recently it was discovered that two species of different genera of halophilic archaea are highly polyploid (Breuert, Allers, Spohn and Soppa 2006, PLoS ONE, e92). A literature survey revealed that the ploidy level has been determined only for a very limited number of species. More than half of them have several copies of the chromosome, indicating that polyploidy might be more widespread in prokaryotes than anticipated. One part of the project will address the distribution of polyploidy. The ploidy level will be determined for about 15 model species representing different phylogentic groups of bacteria. In addition, new isolates from environmental samples will be characterized, and it will be attempted to select for polyploid bacterial species. A second part of the project will address the evolutionary advantage of polyploidy. First, ploidy mutants of halophilic archaea will be selected that can be compared with the wildtype. The resistance against X-ray irradiation and desiccation will be characterized. It will be proven that intracellular polymorphism can yield a selective advantage under specific conditions, and gene conversion will be studied. Taken together, the project challenges the textbook view that prokaryotes are typically monoploid, and it will yield insight into the evolutionary advantage of polyploidy in prokaryotes.